Circulating asialo-glycoproteins are rapidly cleared from the circulation by a mechanism initiated by the binding to a specific hepatic membrane protein and transport into the hepatocyte. This receptor is a major hepatocyte cell surface protein and thus is amenable to studies of its structure, biosynthesis, function and modulation. The receptor, already purified 500-fold over Triton X-100 preparation, will be purified to homogeneity using affinity chromatography and monoclonal antibodies directed at the binding site. The composition of the functional receptor will be examined in terms of the subunits, the number of polypeptides, and associated molecules. Structural studies of orientation of the receptor in the plasma membrane and intracellular organelles will be performed with (125I)-iodination of right-side out and inside-out membrane vesicles, protease digestion and isolation of the products with antibody. Pulse-labelling with (35S)-methionine of isolated hepatocytes will allow examination of orientation in intracellular structures and the time required to reach the cell surface. Cell-free in vitro synthesis with free- and membrane-bound polyribosomes and mRNA will examine the site(s) of biosynthesis. The requirements for membranes in the synthesis of this protein as well as the ultimate structure of the newly made protein will be performed with (35S)-methionine labelling and monoclonal antibody isolation of the products. Function of the receptor will be examined with radioactive-, fluorescent- and ferritin-labelled ligand in isolated hepatocytes; including the relationship of the receptor to coated pits/vesicles and examination of receptor turnover (recycling). Both quantitative (with the use of antibodies) and functional (binding activity) evaluation of the receptor can be performed.